In mammalian physiology, P450 monoxygenase systems participate in the metabolism of steroid hormones, vitamin D, bile acids and a variety of drugs and other xenobiotic substances. Purification and characterization of P450eryK has been of great interest due to its role in erythromycis biosynthesis and the potential to engineer P450eryK to perform new hydroxylations for the development of novel antibiotic analogs.